The present invention relates generally to new and novel improvements in a rotary impact tool having a twin hammer mechanism. More particularly, the present invention relates to a rotary impact tool having a twin hammer mechanism, such as a air driven impact wrench, which is capable of delivering, in rapid succession, a series of rotary impact forces or blows. Such tools have typically been used to tighten or loosen high torque nut or bolts or similar items.
A conventional rotary impact wrench mechanism, known as a xe2x80x9cswinging weightxe2x80x9d mechanism, is disclosed in U.S. Pat. No. 2,285,638 to L. A. Amtsberg, issued Jun. 9, 1942, for an xe2x80x9cImpact Clutch.xe2x80x9d While this mechanism is rather inefficient, it is one of the first to deliver rotary force in a series of impact blows. The ability to deliver a series of impact blows provides a human operator with an advantage in that the human operator can physically hold the impact wrench while delivering high torque forces in short burst or impacts. The advantage of applying short duration high torque impact blows is that a normal human being can continue to physically hold the tool while applying high torque forces. If such high torque forces were applied continuously by the tool, an opposite continuous reaction force on the tool would be too great to allow the tool to be held by a normal human being.
An improved xe2x80x9cswinging weightxe2x80x9d mechanism is disclosed in U.S. Pat. No. 3,661,217 to Maurer, issued May 9, 1972, for a xe2x80x9cRotary Impact Tool and Clutch Therefor,xe2x80x9d the disclosure of which is hereby incorporated by reference. This issued United States patent describes and shows a swinging weight impact wrench mechanism with a hammer member that is substantially free of tensional stresses during impact. This xe2x80x9cswinging weightxe2x80x9d mechanism has a swinging hammer pivoted on a pivot with the center of mass of the hammer being near the center of rotation of the mechanism. This enables the swinging weight mechanism to strike a more balanced blow to an anvil and, ultimately, to the output shaft to tighten or loosen bolts, for example.
However, one problem with the xe2x80x9cswinging weightxe2x80x9d mechanism disclosed in issued U.S. Pat. No. 3,661,217 to Maurer, issued May 9, 1972, for a xe2x80x9cRotary Impact Tool and Clutch Thereforxe2x80x9d is that high loads transmitted through the hammer and the anvil lugs can cause separation of the anvil lugs from the anvil and premature failure of the rotary impact tool.
Accordingly, an object of the present invention is to provide a rotary impact tool having a twin hammer mechanism which is less susceptible to premature failure and, thus, provides enhanced durability and service life as compared to known prior art rotary impact tools.
Another object of the present invention is the provision of a rotary impact tool having a twin hammer mechanism which is capable of applying the same amount of torque to a workpiece with less air consumption as compared to known prior art rotary impact tools.
Yet another object of the present invention is the provision of a rotary impact tool having a twin hammer mechanism which is capable of applying a greater amount of torque to a workpiece while maintaining the size of the housing as compared to known prior art rotary impact tools.
These and other objects of the present invention are attained by a rotary impact tool having a twin hammer mechanism that generally includes a housing having a hollow cage or carrier member positioned therein. A pair of hollow hammer members are pivotally positioned relative to the hollow cage or carrier member so the hollow hammer members rotate with the hollow cage or carrier member under drive from an air motor output shaft. An anvil is positioned inside the hollow hammer members and the anvil rotates relative to the hollow hammer members. The anvil preferably includes a forward anvil lug, a rearward anvil lug, and an annular ring positioned intermediate the forward anvil lug and the rearward anvil lug. To facilitate assembly of the anvil through the hollow hammer members, the annular ring can be a reduced diameter annular ring or the sides of a full diameter annular ring could be reduced or narrowed. Positive spacing of the hollow hammer members can be achieved by placing a spacer between the hollow hammer members. Alternatively, positive spacing of the hollow hammer members can be achieved by extending the hollow hammer members over the annular ring on the anvil with a step provided on each of the hollow hammer members to provide clearance for the annular ring on the anvil.
Other advantages and novel features of the present invention will become apparent in the following detailed description of the invention when considered in conjunction with the accompanying drawings.